Obliquity of tin Ecliptic, 42f 



oftentimes are doubtful. But even those observations, when 

 submitted to sound criticism, may, owing to the distance 

 of time when they were made, throw great light on several 

 important elements of astronomy, and therefore deserve all 

 the attention of geometers and astronomers. 



OF OBSERVATIONS ANTERIOR TO OUR ^ERA. 



Chinese Observations, 



The Chinese observations I am going to relate, are ex- 

 traded from the " Edifying Letters on the History of Chinese 

 Astronomy by the learned Father Gaubil," published bv 

 Father Sauchet, and particularly from a precious manuscript 

 sent from China by the said Father Gaubil in 1/34, which 

 I have published in the Conn, des Terns of 1SOQ. 



The most ancient observation that has reached us, relative 

 to the ecliptic's obli<]uitv, is Tcheou-Kong's, the brother of 

 Vou-vang emperor or China, who, towards the year 1 loo 

 previous to our sera, had occupied himself with particular 

 care in making astronomical observations. After his bro- 

 ther's death, he was regent of the empire, and his memory 

 is still in great veneration among the Chinese, as having 

 been one of the best princes that ever governed. His ob- 

 servations on the length of the gnomon at the solstices are 

 the most ancient astronomical observations that can be used, 

 All anterior observations of eclipses and solstices that have 

 reached us, are related in too vague a way to serve for astro- 

 nomical determinations ; they are of service only to en- 

 lighten chronology ; and if other observations are wanted 

 that can be truly useful to astronomy, we must go back 

 from the epocha of Tcheou-Kong to the time when the 

 lunar eclipse was observed at Rabylon, the year 720 previous 

 to our sera, as related in the Almagestes of Ptolomy. This 

 great antiquity of Tcheou- Kong's observations, and their 

 vast importance, induce me to expect that the details I am 

 about to enter into respecting them will be perused with 

 interest. Here, first of all, is what Father Gaubil records in 

 his History of the Ancient Astronomy of the Chinese, in- 

 serted in the xxvith vol. of.* 4 Edifying Letters," p. 142. 



^Tcheou-Kong, as well as his father prince Ou-en-ouang, 

 and one of his ancestors, prince Kong-hicon, of whom men- 

 tion has been made, took a delight in observing the shadea 

 of gnomons. In the town of Tching-tcheou he drew with 

 care a meridian line, he levelled the ground for observation, 

 he measured the shadow at noon and afternoon; at night he 

 pbser\;ed the pol.ar star. This prince also caused observa- 

 tions 



